1. Field of the Invention
The present invention relates to a new method for irreversibly reacting with, and stabilizing, liquid and gaseous thionyl chloride (SOCl2) and the gaseous decomposition products of thionyl chloride. In particular, the present is drawn to a sorption media for use in surrounding batteries that use liquid thionyl chloride as an active ingredient.
2. Background and Description of Related Art
Thionyl chloride (SOCl2) is a corrosive, fuming, toxic, highly reactive, volatile liquid with a suffocating odor. In spite of these somewhat difficult properties, thionyl chloride is used routinely in the chemical industry in the production of chlorides, acyl chlorides, sulfoxides and many other commodity chemicals. Thionyl chloride is also used as the liquid cathode in numerous designs of commercial lithium primary cells (Li/SOCl2) and batteries, produced mostly for military or other governmental use. While use of thionyl chloride by the chemical industry is centralized, isolated, highly controlled and monitored, its use by battery suppliers necessarily brings people into close proximity with this substance. Since, Li/SOCl2 cells are known to be dangerous if mishandled or abused, the principal concern is to protect people from exposure to SOCl2 which might leak from a battery cell as the result of either corrosion or cell rupture (which may occur due to an electrical short). An average D-size Li/SOCl2 cell can contain several grams of free, liquid SOCl2. xe2x80x9cGetteringxe2x80x9d the thionyl chloride immediately upon leaking would prevent, or at least greatly minimize, the danger of exposure to these materials. (The term xe2x80x9cgetteringxe2x80x9d is hereinafter used to mean a reaction by a specie with one or more materials, typically at a surface, in which the specie is physically and/or chemically bound to the material and thereby removed from its environment.) It is in protecting people and the sensitive components surrounding the battery, that the present invention finds its widest utility.
Several patents discuss the use of activated carbon and zinc oxide as separate agents for absorbing nocuous gases. U.S. Pat. No. 5,451,249 recites activated carbons and zinc oxide as absorbents for removing hydrogen sulfide, organic sulfur, and halogen compounds from a gas stream in landfills. U.S. Pat. Nos. 5,955,393, 5,948,726, and 5,985,790 all discuss use of activated carbon and zinc oxide are suitable materials for absorbing acid gases. Finally, U.S. Pat. No. 6,120,744 suggests the use of zinc oxide on activated carbon as useful for catalyzing a reaction in the gas phase of methanol in the presence of propyne or propadiene. None of the prior art however, teach that thionyl chloride is irreversibly gettered by the combination of an activated carbon, and particularly a carbon absorbent media produced by Calgon Carbon Corporation under the trade designation ASZM-TEDA(copyright), and zinc oxide powder.
It is an object of the present invention to provide a combination of materials for irreversibly gettering thionyl chloride and its gaseous decomposition by-products.
It is another object to provide a method for irreversibly gettering thionyl chloride liquid or gas.
Still another object of the invention is to provide a getter system for packaging with sources of thionyl chloride.
The ideal properties of a getter include: irreversible binding with SOCl2, a high volumetric uptake capacity, high efficiency, non-volatile, air stable, insensitivity to atmospheric poisoning, non-toxic, inexpensive, non-corrosive, and the gettering product is not a liquid or oil that could block further flow or accessibility.
In the application at hand, the getter must operate over the temperature range of xe2x88x9220xc2x0 to 74xc2x0 C. In additional, the getter must be irreversible with respect to thionyl chloride so that the thionyl chloride cannot migrate around the battery compartment and degrade seals or cause corrosion problems. High volumetric uptake capacity is desired because the space available for a getter in a battery compartment is typically extremely limited. Efficiency is desired to minimize corrosion and degradation of mechanical properties, as well as pressure safety issues. In addition, the getter should be non-volatile to prevent migration within the battery compartment, and must be stable in air (since there is air present in the local environment of the battery compartment). Furthermore, poisoning by trace molecular species could present a problem since some materials are known to be reactive with gases such as CO2 present within the local environment. MgO in particular is known to slowly react with CO2 and the metal carbonate formed is unreactive to SOCl2. Finally, a non-toxic getter would make handling and worker exposure easier and less expensive in production. While cost is not an overriding concern, a reasonably priced getter would find more uses in commercial applications. Depending on the flow path for the getter, the physical state of the product may be important. If the gettered product is a thick oil or gel-like material, it could block flow channels preventing further gettering. It is also likely that the getter selected may have use in other commercial applications or storage Li/SOCl2 batteries.